1. The Field of the Invention
The present invention relates to prosthetic joints and, more particularly, to modular interchangeable bone implants to replace articular bone surfaces and methods for installing and replacing the implants.
2. The Relevant Technology
The human body has a variety of movable orthopedic joints such as the knee joint, hip joint, shoulder joint, and the like. These joints are formed by the intersection of two bones. The intersecting end of each bone has one or more condyles consisting of a smooth articular surface that is comprised of cartilage. For example, the knee joint comprises two generally rounded condyles, i.e., lateral and medial condyles that are located at the lower or distal end of the femur. These femoral condyles are disposed above corresponding lateral and medial condyles located at the upper or proximal end of the tibia.
As a result of injury, wear, arthritis, disease or other causes, it is occasionally necessary to replace all or part of an orthopedic joint with an artificial implant. This procedure is referred to as a joint replacement or arthroplasty. For example, a total knee arthroplasty comprises cutting off or resecting the femoral condyles at the distal end of the femur and the tibial condyles at the proximal end of the tibia. Complementary artificial implants, referred to as total condylar implants, are then mounted on the distal end of the femur and the proximal end of the tibia. Where only a portion of a joint is damaged, a partial joint arthroplasty can be performed. In this procedure, one or more artificial implants replace only a portion of a joint. For example, where only one femoral or tibial condyle of the knee joint has been injured, only one of the injured lateral or medial femoral condyles is resected. The corresponding one of the lateral or medial tibial condyles is also resected. Implants replacing only a single condyle, referred to as uni-condylar implants, are mounted on the resected area of the femur and tibia.
Although joint replacement is now a common procedure that has met with popular success, conventional implants and related mounting techniques have significant shortcomings. For example, one problem with conventional joint implants and related techniques for mounting is that it can be difficult to fit, adjust, and/or exchange different implants during the fitting stage. That is, implants come in a variety of different sizes, shapes, and configurations. During the joint replacement procedure, the surgeon may often test a variety of different sized implants to determine the best fit and alignment. As conventional implants are screwed into or pounded onto the bone during placement, the fitting, adjustment, and/or replacement of different conventional implants can be difficult and potentially damaging to the bone.
Another shortcoming with current implants is an inability to easily replace the implant once the implant has been installed. For example, as mentioned above, a partial joint arthroplasty may be required, and a uni-condylar implant installed. Months or years later, the rest of the joint may deteriorate and the uni-condylar implant must be replaced with a total condylar implant. This occurs frequently with the knee. Using current prostheses and methods, replacing a uni-condylar implant with a total condylar implant requires removing the entire uni-condylar implant from the bone (including the anchoring system), drilling or otherwise creating a new hole in the bone to anchor the total joint implant, then installing the total joint implant with a new anchor. Because a new anchoring hole and anchor are required, more bone must be drilled into or otherwise removed, causing more pain for the patient, an increased possibility of infection, a longer recovery time, and generally more risk.
Accordingly, what is needed are implants and related methods for mounting the implants on an articular surface of a joint which enable easier fitting, alignment, testing, and/or replacement of implants. What is also needed are implants and related methods which enable easy replacement of uni-condylar implants with total condylar implants.